The present invention relates to covulcanizable anti-aging agents, which are capable of imparting long-lasting protection from thermal aging and fatigue, and from aging due to the effects of oxygen, to vulcanized rubber products. The anti-aging agents according to the present invention are also distinguished by the fact that they are practically hardly extracted from the vulcanized products by water, by oil and/or petrol, or by hydraulic fluids.
It is known that vulcanized rubber products can be protected by anti-aging agents from environmental effects, which destroy these vulcanized products. Thus, for example, known phenolic, aminic, sulfur-containing or phosphorus-containing anti-aging agents are added in order to improve the thermal stability and shelf life of vulcanized rubber products. These are described in greater detail in Ullmann""s Enzyklopxc3xa4die der technischen Chemie, Volume 8, page 19 et seq., for example.
Moreover, it is known that the volatility of anti-aging agents can be reduced by depositing them on support materials and/or by providing them with reactive groups so that they are copolymerized during the production of the rubber, or by depositing them by grafting on the rubber to be protected before vulcanization. Anti-aging agents which are modified in this manner are described, for example, in JP 61 111 343, by W. Schunk, Gummi, Fasern, Kunstst. 43 (3), (1990), 138-144, by R. H. Kline and J. P. Miller, Rubber Chem. Technol. 46 (1), (1973), 96-105, in EP 466 263, DE 19 718 288 and EP 120 801, by H. Fries, Gummi, Asbest, Kunstst. 40. (1987), 238-258, by D. Braun, R. Rettig, W. Rogler, Angew. Makromol. Chem. 211, (1993), 165-194, in DE-A 3 430 510, by G. Scott and S. M. Tavakoli, Polym. Degrad. Stab. 4 (4), (1982), 279-285, and by A. H. Weinstein, Rubber Chem. Technol. 50 (4), (1977), 650-659.
The disadvantages of the anti-aging agents for vulcanized rubber products which have been known hitherto is first, their volatility or ease of extraction, and second, particularly for modified anti-aging agents, is that they are added during the polymerization of the monomers for the production of the rubber are and, therefore, have an adverse effect on the polymerization reaction (e.g. they reduce the rate of reaction).
The object of the present invention, is thus to provide an anti-aging agent which first does not have an adverse effect on the polymerization of monomers and which second, does not exhibit the volatility and ease of extraction of known anti-aging agents, without the efficacy of the anti-aging agents according to the present invention being reduced compared with that of anti-aging agents which were known hitherto.
The present invention relates to covulcanizable anti-aging agents, which can be produced by the reaction of p-phenylenediamines, which are optionally substituted, and/or of sterically hindered phenols, with bifunctional alkyl, aryl and/or aralkyl compounds and subsequent reaction of the products thus obtained with sulfur and/or with sulfur donor compounds.
Suitable p-phenylenediamines, which are optionally substituted, are those of formula (I): 
where
R1 to R4 are identical or different and represent hydrogen, a straight chain or branched C1-C12-alkyl, a C1-C12-alkoxy, a C1-C12-alkyl-thio, a C1-C12-alkyl-amino, a di-(C1-C12-alkyl)-amino, benzyl, 1,1-di-methylbenzyl or phenyl,
and
R5 represents hydrogen, phenyl, a C6-C12-aryl, a C1-C12-heteroaryl or a C1-C12-alkyl.
C1-C12-alkyl radicals are to be understood to mean all linear, cyclic or branched alkyl radicals containing 1 to 12 C atoms which are known to one skilled in the art, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, n-pentyl, i-pentyl, neo-pentyl, n-hexyl, cyclohexyl, i-hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl radicals, which may in themselves be substituted.
Suitable substituents include halogen, nitro and hydroxyl groups, and also include C1-C12-alkyl, C1-C12-alkoxy, C5-C12 cycloalkyles C6-C12-aryl and C1-C12-heteroaryl radicals, such as benzyl, trimethylphenyl, ethylphenyl, chloromethyl, chloroethyl or nitromethyl radicals.
C1-C12-alkoxy radicals are to be understood to mean all linear, cyclic or branched alkoxy radicals containing 1 to 12 C atoms which are known to one skilled in the art, such as methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, t-butoxy, n-pentoxy, i-pentoxy, neopentoxy and hexoxy radicals, which may themselves be substituted by the aforementioned substituents.
C5-C12-cycloalkyl radicals are to be understood to mean all mono- or polynuclear cycloalkyl radicals containing 5 to 12 C atoms which are known to one skilled in the art, such as cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl and cyclononyl radicals, which may themselves be substituted by the aforementioned substituents.
C6-C12-aryl radicals are to be understood to mean all mono- or polynuclear cycloalkyl radicals containing 6 to 12 C atoms which are known to one skilled in the art, such as phenyl or naphthyl radicals, which may themselves be substituted by the aforementioned substituents.
C1-C12-heteroaryl radicals are to be understood to mean all mono- or polynuclear heteroalkyl radicals which are known to one skilled in the art, and which in addition to 1 to 12 C atoms also contain heteroatoms such as N, S, O and/or P in their aromatic ring system, e.g. pyridinyl, triazinyl, furyl, thienyl, thiazolyl, thiazinyl, pyrrolyl and quinolinyl, which themselves may be substituted by the aforementioned substituents.
A preferred embodiment of p-phenylenediamines of formula (I) are those in which
R1 to R4 represent hydrogen, methyl, ethyl, propyl, t-butyl, 2-propyl, 2-butyl, methoxy, ethoxy, cyclohexyl, benzoyl, phenyl, naphthyl, chlorophenyl or toluyl,
and
R5 represents hydrogen, 2-propyl, 1,3-dimethylbutyl or cyclohexyl.
A preferred embodiment of sterically hindered phenols are those of general formula (II): 
in which
R6 and R7 are identical or different and represent hydrogen, a straight chain or branched C1-C12-alkyl, a bridging C1-C12-alkenyl, or di(cyclopentadiene)diyl,
and
R8 has the meaning of R6 or R7, or represents a C6-C12-arylthio, a branched or straight chain C1-C12-alkylthio, or a grouping of formula: 
with the aforementioned meaning of R6 or R7.
The sterically hindered phenols which are preferably used are those in which
R6 and R7 represent hydrogen, methyl, ethyl, 2-propyl, tert.-butyl, 1,1-dimethylpropyl, cyclohexyl, cyclopentyl, methylene, ethylene, butylene or iso-butylene,
and
R8 denotes hydrogen, methyl, tert.-butyl, 2-propyl, 2-butyl, cyclohexyl, cyclopentyl, nonylthio, dodecylthio or cyclohexylthio.
The p-phenylenediamines and sterically hindered phenols which are used for the production of the anti-aging agents according to the present invention are known to one skilled in the art and are described, for example, by J. G. Gillick, Elastomerics, 120 (8), (1988), 17-19, by K. B. Chakraborty, G. Scott and J. Rekers, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 26 (2), (1985), 31, by J. A. Kuczkowski and J. G. Gillick, Rubber Chem. Technol. 57 (3), (1984), 621-651, by G. Scott, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 25 (1), (1984), 62-63 and by G. Scott, Gummi, Asbest, Kunstst. 31 (12), (1978), 934-938, 940, 966.
Compounds of formulae (III), (IV) and (V) can be used as bifunctional alkyl, aryl and/or aralkyl compounds:
(F1)n-alkanediyl-(F2)m xe2x80x83xe2x80x83(III)
(F1)n-aralkanediyl-(F2)m xe2x80x83xe2x80x83(IV)
(F1)n-arenediyl-(F2)m xe2x80x83xe2x80x83(V)
in which
F1 represents chlorine, bromine, iodine, a hydroxyl, a carbonyl, a carboxyl, an olefin, an alkyne, a sulfate, a sulfonate, a phosphate, a carbonate, an isocyanate or an isothiocyanate,
and
F2 represents a halogen, an olefin, an alkyne, a phosphate or a thiophosphate, hydrogen sulfide, a di- or trisulfane, or a sulfite or thiosulfate,
wherein
the alkanediyl group contains 1 to 30 carbon atoms, can optionally be singly- or multiply-interrupted by hetero atoms, such as oxygen, nitrogen or sulfur, can optionally be substituted by C1-C12-alkyl, C1-C12-alkyloxy, C1-C12-alkyl-thio, C1-C12-alkylamino, di-(C1-C12-alkyl)-amino, benzyl, phenyl or C5-C12-cycloalkyl groups, and can be straight chained, branched or cyclic,
the aralkanediyl group, as well as the arenediyl group, contains 1 to 30 carbon atoms, can optionally be substituted by C1-C12-alkyl, C1-C12-alkyloxy, C1-C12-alkyl-thio, C1-C12-alkyl-amino, di-(C1-C12-alkyl)-amino, benzyl, 1,1-dimethylbenzyl or phenyl, and can contain one or more heteroatoms of the aforementioned type,
and
the suffices n and m are identical or different, wherein 1xe2x89xa6nxe2x89xa610 and 1xe2x89xa6mxe2x89xa610.
n is preferably given by 1xe2x89xa6nxe2x89xa66 and m is preferably given by 1xe2x89xa6mxe2x89xa64, with 1xe2x89xa6nxe2x89xa63 and 1xe2x89xa6mxe2x89xa63 being most preferred.
The F1 and F2 radicals in formulae (III) to (V) can be identical or different.
The following are preferred as the functional group F1: chlorine, bromine, hydroxy, olefin, carbaldehyde or ketone groups, and C2-C30-carboxylates and derivatives thereof, such as C2-halides, anhydrides, esters, amides, isocyanates, sulfates and sulfonates of C30-carboxylic acids.
The following are preferred as the functional group F2: chlorine, bromine, vinyl, allyl, styryl, butanedienyl, cyclopentenyl, cyclohexenyl, cyclooctenyl, cyclooctadienyl, alkynyl, hydrogen sulfide, and di- and trisulfanes.
The preferred alkanediyl groups are: methylene, C2-C30-alkanediyl, C5-C20-cycloalkanediyl, C6-C30-bi-, tri- and tetracycloalkanediyl groups,
The preferred aralkanediyl groups are: phenyl or benzyl which are optionally singly- or multiply-substituted by straight chain or branched C1-C12-alkyl groups.
The preferred arenediyl groups are: phenylene, naphthylene, triazinylene or pyrimidinylene groups which are optionally singly- or multiply-substituted by straight chain or branched C1-C12-alkyl groups.
Examples of compounds of formulae (III) to (V) which are used for the production of the anti-aging agents according to the present invention include C2-C30-dihalogenoalkanes, C2-C30-halogenoalkenes and -alkynes, C2-C30-halogenocarbaldehydes, C2-C30-halogenoketones and C2-C30-halogenocarboxylic acids, unsaturated C3-C30-carbaldehydes, C3-C30-ketones or C3-C30-carboxylic acids which are singly- or multiply-substituted, and C1-C12-alkyl esters, C1-C12-alkyl amides, anhydrides and acid halides thereof.
The following are used in particular: allyl chloride, 1,4-dichloro-2-butene, 2,3-dichloro-1-butene, 3,7-dichlorocycloocta-1,5-diene, 3-cyclohexene carbaldehyde, isophorone, phorone, mesityl oxide, acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, oleic acid, linoleic acid and linolenic acid, and C1-C12-alkyl esters thereof such as methyl, ethyl, propyl, 2-propyl, butyl, 2-butyl, tert.-butyl, 2-ethylhexyl, octyl or dodecyl esters thereof, as well as C1-C12-alkyl amides thereof, such as the N-methyl, N-ethyl, N-propyl, N-2-propyl, N-butyl, N-2-butyl, N-tert.-butyl, N-2-ethylhexyl, N-octyl or N-dodecyl carbamides thereof, as well as the corresponding C2-C24-dialkyl amides containing the aforementioned C1-C12-alkyl amide radicals which can be identical or different.
The aforementioned compounds, which are optionally substituted, can also of course be used in admixture with each other.
According to the present invention, 0.1 to 4, preferably 0.5 to 3, most preferably 1 to 2 mol of bifunctional alkyl and/or aralkyl and/or aryl compounds of formulae (III), (IV), (V) are used per mol of p-phenylenediamines, which are optionally substituted, and/or of sterically hindered phenols.
To produce the covulcanizable anti-aging agents according to the present invention, the reaction product, which is obtained in the manner described above is further reacted with sulfur and/or with sulfur donor compounds.
The sulfur donor compounds, which can be used for the production of the anti-aging agents according to the present invention are compounds which are capable of releasing sulfur during the reaction. These sulfur donors are known to one skilled in the art (see Werner Hofmann, xe2x80x9cKautschuktechnologiexe2x80x9d, Genter Verlag, Stuttgart 1980, 256-258, for example). Compounds which are suitable for this purpose are those which contain one or more direct sulfur-sulfur bonds, such as C1-C30-alkyl di-, tri-, tetra-, penta- and polysulfides or di(C1-C30-alkylamino)-N-di-, xe2x80x94N-tri-, xe2x80x94N-tetra- and N-polysulfides for example.
The sulfur and/or sulfur donor compounds are added to the reaction product which is obtained in an amount such that 1 to 8 mol, preferably 2 to 6 mol, most preferably 3 to 5 mol of sulfur and/or sulfur donor compound are used for each functional group F2. The molar amounts of sulfur to be used are defined here as xe2x85x9 mol S8 (cyclooctasulfur).
As mentioned above, the substituted p-phenylenediamines and sterically hindered phenols can be used in admixture with each other. The most favorable mixture ratio can easily be determined by preliminary tests and depends, for example, on the requisite physical properties of the anti-aging agents. The same applies to the mixture of bifunctional alkyl, aralkyl and aryl compounds which is optionally used, and to the mixtures of sulfur and sulfur-containing compounds which are used.
The reaction of the p-phenylenediamines and/or sterically hindered phenols with the bifunctional alkyl, aralkyl or aryl compounds is usually conducted in the presence of inert, organic solvents.
Examples of suitable inert, organic solvents include: aliphatic or aromatic hydrocarbons which may optionally be substituted with alkyl, alkoxy, halogen, nitro, amino or sulfo groups, as well as aliphatic or aromatic ethers, amines and sulfides.
The following are preferably used as solvents: alkylbenzenes, xylene and petrol of the types, which are known for purposes such as this.
The aforementioned reaction can also, of course, be conducted without a solvent, for example in the melt or in an excess of bifunctional compounds of formulae (III), (IV), and (V) which are present in liquid form.
The most favorable amount of solvent to be used can easily be determined by appropriate preliminary tests.
The first reaction step for the production of the anti-aging agents according to the present invention is usually conducted at temperatures of xe2x88x9220 to +200xc2x0 C., preferably at 40 to 140xc2x0 C.
If the first reaction step is conducted with an excess of bifunctional alkyl, aryl and/or aralkyl compounds, the excess of these compounds is distilled off before further reaction is effected with sulfur and/or sulfur-containing or sulfur donor compounds. When an inert, organic solvent is used, it can remain in the reaction product.
The reaction product, which is obtained in the first reaction step is reacted with sulfur and/or with sulfur-containing compounds at temperatures of about 40 to 200xc2x0 C., preferably at 110 to 160xc2x0 C., most preferably at 130 to 150xc2x0 C.
The production of the anti-aging agents according to the present invention by the reaction described above can, of course, be speeded up by suitable catalysts. Examples of suitable catalysts for the first reaction step include: Lewis acids, such as aluminum, zinc, tin, titanium, iron or boron halides, Brxc3x6nsted acids such as sulfuric and sulfonic acids, hydrochloric acid or phosphoric acid, and also bases such as amines or metal hydroxides, for example sodium, potassium and calcium hydroxides and the aqueous solutions thereof which are known for purposes such as these.
Examples of suitable catalysts for the second reaction include: ammonia, C1-C36-alkyl amines, C2-C40-dialkyl amines and ammonium salts thereof, hydrogen sulfide, di-, tri- and tetrasulfanes and C1-C36-alkyl or C1-C40-dialkyl derivatives thereof, as well as salts of metals of Groups 1, 2 and 12 with C1-C36-dithiocarboxylic acids and (C1-C36-alkyl amides thereof, such as C1-C36-alkyl dithiocarbonates, C1-C36-alkyl dithiocarbamates, (C1-C36-alkyl)-mercaptothiazole or (C1-C36-alkyl)-mercapto-benzothiazoles for example. Other catalysts include salts of metals of groups 1, 2 and 12 with thiosulfuric acids and thiophosphoric acids, with hydrogen sulfide, with di-, tri- and tetrasulfanes, and with selenic, telluric, phosphoric and cyanic acids and hydrogen iodide.
The catalysts are used in customary amounts (0.1 to 10 mol % with respect to one mol of bifunctional compounds of formulae (III), (IV) or (V)).
The anti-aging agent, which is obtained according to the present invention is used as mentioned above for the protection of vulcanized rubber products which are exposed to harmful environmental effects. It is possible, of course, to combine these anti-aging agents with the anti-aging agents which are known to one skilled in the art for the protection of vulcanized rubber products. The most favorable mixture ratio can easily be determined by suitable preliminary tests and depends on the respective purpose of use of the vulcanized products to be protected.
Moreover, it is possible to use the anti-aging agent according to the present invention in admixture with one of the known ozone protection agents in order to achieve improved protection of vulcanized rubber products from ozone. Here also, one skilled in the art can easily determine the most favorable mixture ratio by preliminary tests.
The anti-aging agent according to the present invention is normally used in amounts of 0.5% by weight to 10% by weight, preferably 2% by weight to 5% by weight, with respect to 100 parts of the rubber to be protected.
The rubber compound can also, of course, contain other adjuvant substances for rubber, such as reaction accelerators, thermal stabilizers, light stabilizers, processing aids, plasticizers, tackifiers, foaming agents, colorants, pigments, waxes, extenders, organic acids, retarders, and metal oxides, as well as activators such as triethanolamine, polyethylene glycol or hexanetriol, which are known and which are customary in the rubber industry. These rubber adjuvants are admixed in the customary amounts depending on the intended purpose of use in each case. Examples of customary amounts are 0.1 to 50% by weight with respect to the total amount of rubber used.
Apart from the adjuvant substances mentioned above, known crosslinking agents can be added to the rubber compound, such as sulfur or sulfur donors, and vulcanized production accelerators can be added, such as mercaptobenzthiazoles, benzthiazole sulfenamides, guanidines, thiurams, dithiocarbamates, thioureas and/or thiocarbonates. The vulcanized production accelerators and the aforementioned crosslinking agents are normally used in amounts of 0.1 to 10% by weight, preferably 0.5 to 4% by weight, with respect to the total amount of rubber, which is used in each case.
Vulcanization of rubber compounds containing the anti-aging agents according to the present invention can be effected at the customary temperatures of 100 to 200xc2x0 C., preferably 130 to 180xc2x0 C. (optionally under a pressure of 10 to 200 bar).
Further admixture of the rubbers with the other aforementioned rubber adjuvants, crosslinking agents and accelerators can be effected in the usual manner with the aid of suitable mixing units such as rolls, kneaders and compounding extruders.
The rubber blends which are obtained can optionally be compounded and vulcanized in the usual manner, as is described in more detail in the Encyclopedia of Polymer Science and Engineering, Vol. 4, page 66 et seq. (Compounding) and Vol. 17, page 666 et seq. (Vulcanization), for example.